Synchronized hydraulic servo motor system

ABSTRACT

Hydraulic system for moving common load or separate loads requires all drive members to move in synchronism. Two or more hydraulic servo motors are each provided with a hydraulically movable drive member. A synchronizing valve is interposed either in the conduit from the pressure fluid supply to each motor or in the conduit from each motor to the fluid reservoir to modulate the flow to its associated motor and includes two valve members which move with and with respect to each other. One valve member of each valve is attached to the drive member of its associated motor and the other valve member is attached to the drive member of the next preceding or succeeding motor so that all of the valves and motors are connected in a mechanical &#39;&#39;&#39;&#39;closed-loop&#39;&#39;&#39;&#39; series. When all motors are in synchronism, the two members of each valve move in the same direction in synchronism and do not affect the fluid flow. If any motor advances ahead of synchronism, the members of its associated valve are caused to move with respect to each other by mechanical linkages to restrict fluid flow and retard the leading motor until it is returned to synchronism. The system may be designed to onedirection operation or two-direction operation. In the onedirection system, a closed loop arrangement is not essential. In a modification, the valve porting may be arranged to restrict flow to the leading motor and also increase flow to the lagging motor to accelerate the return to synchronism. In a further modification, the porting may be shaped to give varying rates of change of flow for each increment of relative movement.

Unite r S taes Howarth et a1.

1 tent [I91 1 SYNCHRONlZED HYDRAULHC SERVO MOTOR SYSTEM [75] Inventors:Roger E. Howarth; William M.

McGuigan, both of San Diego, Calif.; David A. Murday, Oxhey Watford.Herts County, England [73] Assignee: Rohr Corporation, Chula Vista,

Calif.

[22] Filed: June 1, 1971 [21] Appl. No.: 148,740

Primary Examiner-Paul E. Maslousky Attorney-George E. Pearson [57]ABSTRACT Hydraulic system for moving common load or separate loadsrequires all drive members to move in synchronism. Two or more hydraulicservo motors are each provided with a hydraulically movable drivemember. A synchronizing valve is interposed either in the conduit fromthe pressure fluid supply to each motor or in the conduit from eachmotor to the fluid reservoir to modulate the flow to its associatedmotor and includes two valve members which move with and with respect toeach other. One valve member of each valve is attached to the drivemember of its associated motor and the other valve member is attached tothe drive member of the next preceding or succeeding motor so that allof the valves and motors are connected in a mechanical closed-loopseries. When all motors are in synchronism, the two members of eachvalve move in the same direction in synchronism and do not affect thefluid flow. If any motor advances ahead of synchronism, the members ofits associated valve are caused to move with respect to each other bymechanical linkages to restrict fluid flow and retard the leading motoruntil it is returned to synchronism. The system may be designed toone-direction operation or two-direction operation. In the one-directionsystem, a closed loop arrangement is not essential. In a modification,the valve porting may be arranged to restrict flow to the leading motorand also increase flow to the lagging motor to accelerate the return tosynchronism. In a further modification, the porting may be shaped togive varying rates of change of flow for each increment of relativemovement.

12 Claims, 9 Drawing Figures I 1 1 I l 4 6 --=='IA E g- Patented Sept.4, 1973 3,756,123

5 Sheets-Sheet 1 INVENTOR. ROGER E, HOWARTH WILLIAM M. MCGUIGAN DAVID A.MURD? BY W ATTORNEY Patented Sept. 4,1973

3 Sheets-Sheet 5 I 139 I24 "/{fIZSO 'TEQQEF FIG. 5

INVENTOR. ROGER E. HOWARTH WILLIAM M. McGUIGAN DAVID A. MUiR\D(/-\DY ,BYw 2- Mm.

ATTORNEY SYNCI-IRONIZED HYDRAULIC SERVO MOTOR SYSTEM BACKGROUND OF THEINVENTION This invention lies in the field of hydraulic servo motoractuation and control and is directed to systems in which two or moresuch motors are actuated at the same time and connected to a common loador to separate loads. In most installations it is highly desirable oressential that the motors be very accurately synchronized so that theload or loads will be moved in unison. One example is a jet engine podinstallation having a large ejector barrel which must be moved axially.Usually two or more servo motors are arranged in spaced relation aroundthe periphery of the pod and connected to the forward end of the ejectorbarrel. If one of the servo motors advances ahead of synchronism it willtend to cock the ejector barrel and cause it to bind in its tracks. Thisincreases the total force required and may cause damage to the tracks orother components.

Another typical example is an airplane provided with lift-increasingflaps. Since the flaps are spaced at opposite sides of the fuselage,they are normally actuated by separate servo motors. If one flap bindsin its mountings the other flap will be extended angularly ahead of it,causing a high rolling moment which may be difficult or impossible tocounteract with ailerons or other available controls.

In both of the examples above, it is necessary to provide some type ofsynchronization to prevent the undesirable consequences. Many systemshave been devised, including mechanical interconnection through gearingor linkages, and hydraulic or mechanical feedback devices to modulatethe fluid flow to the various servo motors. These systems have in themain been quite operable and performed their functions in a generallysatisfactory manner. The principal drawback has been undue complicationand maintenance cost.

SUMMARY OF THE INVENTION The present invention is directed to a totalsynchronized system which performs the ultimate functions of theprevious systems in a simple and straightforward manner with a minimumof relatively simple and duplicate parts, reducing both initial cost andmaintenance, and insuring reliable operation.

Generally stated, two'or more hydraulic servo motors are provided, eachof which has a hydraulically movable drive member. All of the drivemembers may be connected to a single load or they may each drive aseparate load, but in either case they are required to move insynchronism to accomplish their purpose. One or more sources of pressurefluid are connected by separate conduits to each motor, and asynchronizing valve is interposed in each conduit to modulate the flowof fluid to its associated motor.

Each valve includes a pair of valve members which are movable with andwith respect to each other, at least one of the members having a fluidport and the other member having means to restrict the area of the portopening to varying degrees. One valve member is drivenly connected tothe drive member of its associated motor and the other valve member isdrivenly connected to the drive member of the next adjacent motor whichmay be considered as the preceding or succeeding one. The relativephysical location of the components may be whatever is required by anyparticular installation but the operational relation is such that themotors and valves are alternately arranged sequentially so that everyvalve is between two motors and every motor is between two valves. Thusit may be stated that the components are arranged in a. mechanical"closedloop series.

With this arrangement and with. all of the motors operatingsynchronously, the drive members of any two successive motors wll causethe two valve members of the intermediate valve to move in the samesense or direction at the same rate so that there will be no relativemovement away from neutral, synchronized relation and fluid flow willnot be affected. However, if any motor advances ahead of synchronism,its drive member will move its connected valve member at a greater rateto produce relative movement of the two members of the preceding andsucceeding valves. The members are so designed and arranged that thisrelative movement in the valve associated with the leading motor willrestrict the flow of fluid to that motor and retard its movement untilit is returned to synchronism. However, the relative movement in theother valve will not restrict fluid flow to the lagging motor, and thusthe latter will, in effect, catch up" with the leading motor. In amodification, the porting is so designed that in neutral, synchronizedrelation the one valve member partially restricts the flow controllingport of the other valve member. However, the port is large enough sothat its restricted area is sufficient to allow the designed normal rateof flow. Relative movement in such a valve associated with the laggingmotor is in the opposite sense to that of the leading motor valve, andthe flow is increased to the lagging motor to accelerate the return tosynchronism.

The principle of operation described above may be applied to valveshaving linear motion or rotary motion and to either one-direction ortwo-direction actuation with appropriate design changes. In the case ofonedirection actuation, a closed loop arrangement is not essential. Thecomponents may be arranged diagrammatically in a line with one lessvalve than the number of motors. Then one motor is the master and theother motors are slaves.

BRIEF DESCRIPTION OF THE DRAWINGS Various other advantages and featuresof novelty will become apparent as the description proceeds inconjunction with the accompanying drawings, in which:

FIG. I is a schematic illustration of a system in accordance with theinvention with two servo motors and two synchronizing valves of therotary type;

FIG. 2 is a schematic section view taken on line 2-2 of FIG. 1;

FIG. 3 is a view similar to FIG. 2 showing a modification;

FIG. 4 is a view similar to FIG. 1 but incorporating linear motionvalves;

FIG. 5 is a view similar to FIG. 4 but showing a twodirectionarrangement;

FIG. 6 is a view similar to FIG. 5 showing a different form oftwo-direction arrangement;

FIG. 7 is a schematic sectional elevation view of a valve havingvariable porting;

FIG. 8 is a schematic sectional plan view of the valve of FIG. 7, takenon the line 8-8 of FIG. 7; and

FIG. 9 is a graph illustrating the flow variation through the valve ofFIG. 7.

DESCRIPTION OF PREFERRED EMBODIMENTS The assembly shown schematically inFIG. 1 includes a first servo motor 10, a second servo motor 12, a firstvalve 14, and a second valve 16. Fluid under pressure flows from asource 18 through a conduit 20 to and through first valve 14 and thencethrough conduit 22 to the associated first motor 10. Fluid also flowsthrough conduit 24 to and through second valve 16 and thence throughconduit 26 to the associated second motor 12.

Fluid entering chamber 28 of motor drives the piston 30 to the right asviewed in FIG. 1 together with drive member 32, the fluid at theopposite side of the piston exiting through conduit 34 and returning bya path, not shown, to a reservoir at source 18. The drive member isconnected by link 36 to the lever arm 38 of the rotatably mounted member40 which is representative of the load to be moved by motor 10. Rotationof load member 40 causes rotation of linkage 42 in the directionindicated by the arrow, and the linkage in turn rotates valve member 44in the same sense or direction.

Motor 12 operates in the same manner as motor 10 to pull its drivemember 46 to the left as viewed in FIG. 1, and the drive member actsthrough link 48, lever arm 50 and load member 52 to rotate linkage 54 inthe direction indicated by the arrow, and the linkage in turn rotatesvalve member 56 in the same sense or direction as valve member 44. Itwill be apparent that drive members 32 and 46 act in the same waythrough linkages 58 and 60 to rotate valve members 62 and 64 in thedirection indicated by the arrows. Thus it will be seen that the motorsand valves are mechanically connected together in alternate arrangementto form a mechanical closed-loop series. There may be any number ofmotors and associated synchronizing valves in the series and they may belocated where needed or convenient, the rotating linkages beingappropriately designed to make the operative connections. If necessaryor desired, the valves may be mounted in static outer cases as indicatedat 66.

It will be seen that with respect to valve 14, drive member 32 isconnected to valve member 44 which is the core, while drive member 46 isconnected to valve member 56 which is the sleeve. On the contrary withrespect to valve 16, drive member 32 is connected to sleeve 62 and drivemember 46 is connected to core 64. When pressure fluid is supplied fromsource 18, both motors act in unison and rotate both members of eachvalve in the same direction at the same rate. Thus there is no relativemovement between them and no modulation of the pressure fluid flow.However, if the first motor 10, for instance, advances ahead ofsynchronism, or leads, it will cause core 44 and sleeve 62 to leadsleeve 56 and core 64. The effect of this action will be explained withreference to FIGS. 1 and 2 in conjunction.

First considering valve 14, core 44 has an inlet port 68 connected toconduit 20 and leading to the interior of the core. Near its oppositeend the core is provided with a port 70 which extends a substantialdistance peripherally and is in registry with port 72 of sleeve 56. InFIG. 2 the valve members are shown in neutral or synchronized relationwith port 72 overlying the one end of port 70 and with the lip 74 of thecore aligned with one edge of port 72. As shown the valve members arerotating clockwise at the same rate and port 72 is wide open. However,when motor 10 leads motor 12, it causes core 44 to lead sleeve 56 sothat lip 74 begins to overlap port 72 as indicated in FIG. 3 andrestrict the flow through 72 and conduit 22 to motor 10. This retardsmotor 10 until it falls back into synchronism, which also returns thevalve members to the relation of FIG. 2 with a wide open port.

The valve members of valve 16 under the same circumstances are rotatingcounterclockwise as viewed in FIG. 2, and when motor 10 leads motor 12it causes core 64 to lead sleeve 62 counterclockwise. However, in thiscase an adjacent portion of port registers with port 72 and the latterremains wide open so that fluid flow through conduit 26 to motor 12 isunrestricted and the motor continues to move at the normal pace until itis back in synchronism with motor 10.

It should be understood that in this and all other forms of theinvention, if the lagging motors are substantially slowed down byfriction or obstructions the valve of the leading motor will increaseits flow restriction up to the point of motor stoppage if necessary tocorrect the difficulty, thus diverting all of the fluid force to thelagging motors.

FIG. 3 further illustrates a modification of the basic valve which isuseful for accelerating correction. In this case, port 72 is made largerin cross sectional area than necessary for the normal design rate offlow and core 44 in neutral position is so located that lip 74 forms apartial restriction, but the unrestricted area is sufficient for normalflow. Thus, when core 44 leads sleeve 56 clockwise in one valve such as14 it restricts flow to its motor and at the same time the core of theother valve leads the sleeve counterclockwise, enlarging the port toprovide abnormal flow to the lagging motor and accelerate thecorrection.

The system shown in FIG. 4 is substantially identical in principle tothe system of FIG. 1 but employs linear motions throughout. The firstservo motor 76 is fed with pressurized fluid flowing from source 78through conduit 80, first valve 82, and conduit 84. Second servo motor86 similarly is fed with pressurized fluid from source 78 throughconduit 88, second valve 90, and conduit 92. The first valve 82 includessleeve 94 and core 96, while the second valve includes core 98 andsleeve 100. The drive member 102 of motor 76 is connected to push-pulllinkages 104 and 106, and the drive member 108 of motor 86 is connectedto push-pull linkages 110 and 112. Cores 96 and 98 are shown in neutralposition immediately adjacent to ports 114 and 116 in sleeves 94 and100.

When fluid pressure is applied, all of the components move in aclockwise direction as indicated by the arrows at a uniform rate. Ifmotor 76 advances ahead of synchronism, drive member 102, pulling onlinkage 104, will cause sleeve 94 to lead core 96 and the latter willbegin to overlap port 114, restricting fluid flow through conduit 84 toretard motor 76. At the same time, drive member 102, pushing on linkage106, will cause core 98 to lead sleeve 100, but in this case the coremoves away from the port and there is no restriction. Therefore motor 86will not be retarded and synchronism will be achieved. The cores may beset to partially restrict the ports 114 and 116 in neutral position asexplained with reference to FIG. 3 to accelerate the return tosynchronism.

area will increase at a varying rate to a maximum and then drop off veryrapidly to zero as the ports go out of registry. The variation in flowrate is illustrated in the graph of FIG. 9. The shapes shown are merelyillustrative, and suitable designs may be worked out to produce anydesired pattern of flow variation. The same type of variable flowcontrol can be used in the rotary valve systems.

It will be apparent that the various forms of the invention illustratedand described herein provide a very effective system for synchronizing aplurality of servo motors. It is particularly advantageous for use ininstallations having a plurality of pressure fluid sources which maytend to operate at different flow rates or pressures. The regulatingunits are quite simple and relatively inexpensive to manufacture andmaintain, and their simplicity insures reliable operation.

Having thus described the invention, what is claimed as new and usefuland is desired to be secured by U. S. Letters Patent is:

l. A synchronized hydraulic servo motor system comprising:

a plurality of hydraulic servo motors adapted to operate in synchronismand each having a hydraulically movable drive member connected to aload; pressure fluid supply means; conduit means connecting the fluidsupply means to the motors and at least two synchronizing valve meansinterposed in the conduit means; each value means comprises two valvemembers movable together in synchronism and movable separately withrespect to each other out of synchronism and mechanically connected toat least two separate drive members each of said drive members connectedto one movable member from each of said valve means to be driventhereby; the advance of any drive member ahead of synchronism causingmovement of the valve members with respect to each other to restrictfluid flow to the motor associated with such drive member and retard itsmovement until it is returned to synchronism.

2. A system as claimed in claim 1; the relative movement of the valvemembers out of synchronism acting to increase fluid flow to at least onelagging motor to accelerate the return to synchronism.

3. A synchronized hydraulic servo motor system comprising:

at least two hydraulic servo motors adapted to operate in synchronismand each having a hydraulically movable drive member connected to aload; pressure fluid supply means; conduit means connecting the fluidsupply means to each of the motors; and a synchronizing valve interposedin the conduit means between the pressurized fluid supply and eachmotor; each valve including first and second valve members movable withand with respect to each other and a flow path extending through thevalve, with the valve members so constructed and arranged that relativemovement in a first sense restricts flow and relative movement in asecond, opposite, sense does not restrict flow; all of the valves andmotors being arranged in a mechanical closed-loop series with each valvebetween succeeding motors and each motor between succeeding valves, andwith one valve member of each valve drivenly connected to the drivemember of the preceding motor and the other valve member drivenlyconnected to the drive member of the succeeding motor; the advance ofthe drive member of any motor ahead of synchronism causing relativemovement of the valve members in the first sense in its associated valveto restrict fluid flow to such motor and retard its movement until it isreturned to synchronism.

4. A system as claimed in claim 3; the advance of the drive member ofsuch motor ahead of synchronism further causing relative movement of thevalve members in the second, opposite, sense in the valves associatedwith the next adjacent motor to increase fluid flow to it and acceleratethe return to synchronism.

5. A system as claimed in claim 3; in which one valve member of eachvalve is a sleeve having at least one port, and the other valve memberis a core coaxially mounted within the sleeve and movable with and withrespect to the sleeve; the core being relatively movable to positionsrestricting the opening in the port in varying degrees.

6. A system as claimed in claim 5; the valve members having a neutral,synchronized position in which the core partially restricts the port;the core being movable relative to the sleeve in one sense to furtherrestrict the port and in the opposite sense to reduce the restriction ofthe port.

7. A system as claimed in claim 5; in which the valve members are causedto move linearly on their common longitudinal axis in the same directionby the drive members of adjacent motors.

8. A system as claimed in claim 5; in which the valve members are causedto rotate about their common axis in the same direction by the drivemembers of adjacent motors.

9. A system as claimed in claim 8; in which a first valve member has aport of predetermined size and the second valve member has a port ofgreater size elongated about the periphery, and in neutral, synchronizedposition the first port is located substantially at one end of thesecond port; the second port being relatively movable in one directionto restrict the second port and relatively movable in the oppositedirection without restricting the first port.

10. A system as claimed in claim 3; in which one valve member of eachsynchronizing valve is a sleeve having an inlet port and an outlet port,and the other valve member is a core coaxially mounted within the sleeveand relatively movable to positions restricting the opening in at leastone of said ports; first and second conduits leading from the outletport of each synchronizing valve to first and second adjacent motors; afirst check valve in the first conduit openable under fluid pressure toallow fluid from the outlet port to the first motor; a second checkvalve in the second conduit to block fluid flow from the outlet port tothe second motor; the elements being so connected and arranged thatadvance of the drive member of the first motor ahead of synchronism willcause the core to restrict at least one port in the sleeve to restrictfluid flow to the first motor and retard its action until it is returnedto synchronism; and means to reverse fluid flow through the motors andsynchronizing valves; the first check valve blocking return flow fromthe first motor to the outlet port and the second check valve opening inresponse to fluid pressure to allow fluid flow from the second motor tothe outlet port to provide twodirection actuation of the motors; thesynchronizing The synchronizing system of FIGS. 1 to 4 operates in onedirection only, as shown, and a closed loop arrangement is notessential. The components may be arranged in a line with one less valvethan motors, and then one motor is the master and the other motors areslaves.

The construction of FIG. 5 shows that more than two sets of motors andvalves may be used in a system and also illustrates one suitablearrangement for synchronizing operations in two opposite directions. Inthis case, servo motors 1 18, 120, and 122 are provided with drivemembers 124, 126 and 128 respectively, and the drive members areconnected by linkages 130 to the valve members in the same way as thecorresponding elements in FIG. 4. Since all of the units operate in thesame way, the description will be limited to motor 118 and valves 132and 134.

In the neutral condition shown, pressure fluid flows from source 136through conduit 138 and port 140 to and through valve 132 and thencethrough conduit 142 to motor 118. A check valve 144 in line 142 yieldsto allow the flow to motor 118 while another check valve 146 in conduit148 prevents flow to motor 122. A return conduit 150 leads from motor118 back to source 136, and a two-way control valve 152 interposed inconduits 138 and 150 provides for reverse flow to actuate motor 118 inthe opposite direction. Similar conduits and valves are connected fromthe source to the other motors.

When pressure fluid is provided, the entire assembly moves in a counterclockwise direction. If motor 118 new advances ahead of synchronism itsdrive member 124, through linkage 130 will pull core 154 of valve 132and cause it to lead sleeve 156, thus restricting flow through port 140to motor 118 and retarding the latter. At the same time, drive member124, through linkage 130, will push sleeve 158 of valve 134 and cause itto lead core 160 but this will not restrict flow through valve 134 tomotor 120.

When valve 152 is swung to reverse flow position, fluid will flow fromsource 136 through conduit 150 to motor 118. The exhaust fluid from themotor cannot pass check valve 144 and therefore flows through conduit162 to valve 134. It overcomes check valve 164 readily because of thelow pressure in the return line. The other two motors and their newsynchronizing valves operate in the same way. In this case the entireassembly moves in a clockwise direction. If motor 118 now starts tolead, it will pull sleeve 158 through linkage 130 and cause it to leadcore 160 which will therefore restrict return flow through port 166 andretard motor 118. It will also cause core 154 to lead sleeve 156 butthis will not restrict port 140. Thus it will be seen that the assemblyoperates in the same way regardless of the direction of travel.

The system shown in FIG. 6 is similar in layout to the one in FIG. 4 butis designed for two-direction operation. Again there is a first servomotor 168 with a drive member 170 and a second servo motor 172 with adrive member 174, and linkages 176 connecting the drive members withsynchronizing valves 178 and 180. A source of supply, not shown,provides pressurized fluid to conduits 182 and 184 leading to valves 178and 180, and conduits 186 and 188 deliver the exhaust fluid to thereturn line. Valve 178 includes a core 190 and a sleeve 192 which isprovided with longitudinally spaced inlet ports 194, 196 andlongitudinally spaced outlet ports 198, 200. The core is neutrallylocated between the two inlet ports and extends the full distance between them so that any longitudinal relative motion will restrict oneport or the other. The outlet ports could be spaced the same as theinlet ports if desired.

Conduit 202 leads from port 198 to the rod end of motor 168 and conduit204 leads from port 200 to the head end of the motor. A spool valve 206is interposed in these conduits and is shown set for operation in aselected direction, in which conduit 202 has a free path through thevalve while the supply end of conduit 204 is cut off from the motor, andthe motor end of conduit 204 is connected through the spool valve toexhaust conduit 186. The relation of valve to motor 172 is exactly thesame and need not be discussed.

With all parts in the position shown, fluid from the source will flowthrough valves 178 and 180 to the rod ends of motors 168 and 172 andcause the entire assembly to move counter clockwise as indicated by thearrows with the synchronizing valves remaining in neutral relation. Ifmotor 168 should advance ahead of synchronism it will pull core throughlinkage 176 and cause it to lead sleeve 192. The core will then restrictport 194 and the flow through conduit 202, thus retarding motor 168. Atthe same time the drive member 170 will push sleeve 208 through linkage176 and cause it to lead core 210. The core will restrict port 212 butmove away from port 214 which is at this time supplying the open line tomotor 172. Therefore the latter will not be retarded.

For operation in the reverse direction, the spool valve stem 216 ispushed to the left which opens conduit 204 from port 200 to the head endof the motor 168 and connects the motor end of conduit 202 to exhaustconduit 186. A similar change of connections is produced in the circuitof motor 172. When pressure fluid is now provided, the assembly willmove clockwise. If motor 168 now advances ahead of synchronism, drivemember 170 will push core 190 through linkage 176 and cause it to leadsleeve 192 which also causes it to restrict port 196, thus restrictingflow through conduit 204 and retarding motor 168. At the same time drivemember 170 will pull sleeve 208 through linkage 176 and cause it to leadcore 210. The latter will then restrict port 214 but move away from port212 which is supplying the open line to motor 172. Therefore, the latterwill not be retarded.

A modified form of synchronizing valve is illustrated in FIGS. 7 and 8,and its principle can be applied to any of the systems previouslydescribed. In this form a sleeve 218 is provided with duplicate inletand outlet ports 220, the inner ends 222 of which have a selected crosssectional shape, here shown as a rectangle. The linearly slidable core224 is in the form of a flat plate slidable in recess 226. Generallycentrally located in the plate is a port 228 which, in planform,comprises a combined triangle and rectangle. The valve members are shownin their neutral position and it will be observed that the solid portionof the core blocks off the ends of the port 222, leaving open the shadedarea 230. This area is sufficient to provide the normal design flow tooperate the servo motors at the desired rate.

If the core is assumed to be stationary and the sleeve is moved to theleft as viewed in FIGS. 7 and 8, port 222 will move toward the narrowend of port 228 and the common flow area will decrease at a varyingrate. If sleeve 218 is moved to the right the common flow valve servingto control fluid flow to the second motor during reverse flow operation.

11. A system as claimed in claim 3; in which one valve member of eachsynchronizing valve is a sleeve and the other valve member is a corecoaxially mounted within the sleeve; each sleeve having twolongitudinally spaced inlet ports and two longitudinally spaced outletports; the core in neutral, synchronized position lying generallycentrally between the ports and being movable longitudinally in eitherdirection to restrict at least one of the ports; conduits extending fromeach of the outlet ports of each synchronizing valve to its associatedmotor; a direction control valve interposed in bothconduits to eachmotor to selectively connect one of them to the motor for actuation inthe selected direction; the motors and their associated synchronizationvalves being so connected that advance of any motor ahead ofsynchronization in either direction will actuate its associatedsynchronizing valve to restrict fluid flow to the motor to retard itsmovement until it is returned to synchronism.

12. A system as claimed in claim 3; each of the valve members of eachvalve having a port for fluid flow; the ports being of different crosssectional shapes and at least partially overlying each other in neutral,synchronized position to provide a common flow area sufficient fornormal fluid flow; the valve members being so arranged that relativemovement in one sense restricts fluid flow at varying rates and relativemovement in the opposite sense enlarges the common area to increasefluid flow at varying rates.

1. A synchronized hydraulic servo motor system comprising: a pluralityof hydraulic servo motors adapted to operate in synchronism and eachhaving a hydraulically movable drive member connected to a load;pressure fluid supply means; conduit means connecting the fluid supplymeans to the motors and at least two syncHronizing valve meansinterposed in the conduit means; each value means comprises two valvemembers movable together in synchronism and movable separately withrespect to each other out of synchronism and mechanically connected toat least two separate drive members each of said drive members connectedto one movable member from each of said valve means to be driventhereby; the advance of any drive member ahead of synchronism causingmovement of the valve members with respect to each other to restrictfluid flow to the motor associated with such drive member and retard itsmovement until it is returned to synchronism.
 2. A system as claimed inclaim 1; the relative movement of the valve members out of synchronismacting to increase fluid flow to at least one lagging motor toaccelerate the return to synchronism.
 3. A synchronized hydraulic servomotor system comprising: at least two hydraulic servo motors adapted tooperate in synchronism and each having a hydraulically movable drivemember connected to a load; pressure fluid supply means; conduit meansconnecting the fluid supply means to each of the motors; and asynchronizing valve interposed in the conduit means between thepressurized fluid supply and each motor; each valve including first andsecond valve members movable with and with respect to each other and aflow path extending through the valve, with the valve members soconstructed and arranged that relative movement in a first senserestricts flow and relative movement in a second, opposite, sense doesnot restrict flow; all of the valves and motors being arranged in amechanical ''''closed-loop'''' series with each valve between succeedingmotors and each motor between succeeding valves, and with one valvemember of each valve drivenly connected to the drive member of thepreceding motor and the other valve member drivenly connected to thedrive member of the succeeding motor; the advance of the drive member ofany motor ahead of synchronism causing relative movement of the valvemembers in the first sense in its associated valve to restrict fluidflow to such motor and retard its movement until it is returned tosynchronism.
 4. A system as claimed in claim 3; the advance of the drivemember of such motor ahead of synchronism further causing relativemovement of the valve members in the second, opposite, sense in thevalves associated with the next adjacent motor to increase fluid flow toit and accelerate the return to synchronism.
 5. A system as claimed inclaim 3; in which one valve member of each valve is a sleeve having atleast one port, and the other valve member is a core coaxially mountedwithin the sleeve and movable with and with respect to the sleeve; thecore being relatively movable to positions restricting the opening inthe port in varying degrees.
 6. A system as claimed in claim 5; thevalve members having a neutral, synchronized position in which the corepartially restricts the port; the core being movable relative to thesleeve in one sense to further restrict the port and in the oppositesense to reduce the restriction of the port.
 7. A system as claimed inclaim 5; in which the valve members are caused to move linearly on theircommon longitudinal axis in the same direction by the drive members ofadjacent motors.
 8. A system as claimed in claim 5; in which the valvemembers are caused to rotate about their common axis in the samedirection by the drive members of adjacent motors.
 9. A system asclaimed in claim 8; in which a first valve member has a port ofpredetermined size and the second valve member has a port of greatersize elongated about the periphery, and in neutral, synchronizedposition the first port is located substantially at one end of thesecond port; the second port being relatively movable in one directionto restrict the second port and relatively movable in the oppositedirection without restricting the first port.
 10. A system as claimed inclaim 3; in which one valve member of each Synchronizing valve is asleeve having an inlet port and an outlet port, and the other valvemember is a core coaxially mounted within the sleeve and relativelymovable to positions restricting the opening in at least one of saidports; first and second conduits leading from the outlet port of eachsynchronizing valve to first and second adjacent motors; a first checkvalve in the first conduit openable under fluid pressure to allow fluidfrom the outlet port to the first motor; a second check valve in thesecond conduit to block fluid flow from the outlet port to the secondmotor; the elements being so connected and arranged that advance of thedrive member of the first motor ahead of synchronism will cause the coreto restrict at least one port in the sleeve to restrict fluid flow tothe first motor and retard its action until it is returned tosynchronism; and means to reverse fluid flow through the motors andsynchronizing valves; the first check valve blocking return flow fromthe first motor to the outlet port and the second check valve opening inresponse to fluid pressure to allow fluid flow from the second motor tothe outlet port to provide two-direction actuation of the motors; thesynchronizing valve serving to control fluid flow to the second motorduring reverse flow operation.
 11. A system as claimed in claim 3; inwhich one valve member of each synchronizing valve is a sleeve and theother valve member is a core coaxially mounted within the sleeve; eachsleeve having two longitudinally spaced inlet ports and twolongitudinally spaced outlet ports; the core in neutral, synchronizedposition lying generally centrally between the ports and being movablelongitudinally in either direction to restrict at least one of theports; conduits extending from each of the outlet ports of eachsynchronizing valve to its associated motor; a direction control valveinterposed in both conduits to each motor to selectively connect one ofthem to the motor for actuation in the selected direction; the motorsand their associated synchronization valves being so connected thatadvance of any motor ahead of synchronization in either direction willactuate its associated synchronizing valve to restrict fluid flow to themotor to retard its movement until it is returned to synchronism.
 12. Asystem as claimed in claim 3; each of the valve members of each valvehaving a port for fluid flow; the ports being of different crosssectional shapes and at least partially overlying each other in neutral,synchronized position to provide a common flow area sufficient fornormal fluid flow; the valve members being so arranged that relativemovement in one sense restricts fluid flow at varying rates and relativemovement in the opposite sense enlarges the common area to increasefluid flow at varying rates.